As illustrated in FIG. 8, a liquid crystal display typically includes a pixel substrate 101 which includes a TFT (Thin Film Transistor) device layer 106, a pixel electrode layer 109, a planarizing layer 108 and an alignment film 103A formed thereon, and a facing substrate 102 which is formed so as to face the pixel substrate 101, and includes a BM (Black Matrix) layer 107, a CF (Color Filter) layer 110, a common electrode 111 and an alignment film 103B formed thereon, and a liquid crystal layer 104 which is formed between both of the above-described substrates. Moreover, a seal layer 105 is arranged between both of the above-described substrates so as to prevent a liquid crystal from being leaked and to adhere the substrates to each other.
As a method of forming a liquid crystal layer between a pixel substrate and a facing substrate in a liquid crystal display with such a configuration, a vacuum injection method in which a liquid crystal is injected after bonding the pixel substrate and the facing substrate together is typically used; however, the method needs a long time to inject the liquid crystal, so there is an issue that in the case where the areas of the substrates are larger, productivity becomes poor.
To solve the issue, a novel method called an ODF (One Drop Fill; liquid crystal dropping) method has been proposed. For example, Patent Document 1 discloses a method of dropping a liquid crystal material onto one of two substrates before bonding the two substrates together for sealing. Moreover, Patent Document 1 also discloses the use of an UV (Ultraviolet) curable sealing agent instead of a thermosetting sealing agent as a material (a sealing agent) forming a seal layer in the ODF method.
Now, the ODF method will be briefly described below. First, a pixel substrate and a facing substrate are prepared. A plurality of gate wires and a plurality of data wires which horizontally and vertically intersect one another to define a pixel region are formed on the pixel substrate. A TFT device is formed at each of intersections of the above-described gate wires and the above-described data wires, and a pixel electrode connected to the above-described TFT device is formed in the pixel region.
A BM layer for blocking the leakage of light in the above-described gate wires, the above-described data wires and a TFT formation region, and red, green and blue CF layers are formed on the facing substrate, and a common electrode is formed thereon. Alignment films for initial liquid crystal alignment are formed on the above-described pixel substrate and the above-described facing substrate.
Next, after the pixel substrate is coated with a sealing agent in the shape of a frame, a liquid crystal layer is formed by dropping a liquid crystal into the frame. In the ODF method, an UV curable (or an UV curable/thermosetting) sealing agent is typically used. It is because in a step of curing the sealing agent in a later step, in the case where a thermosetting sealing agent is used as the sealing agent in a state in which the liquid crystal layer is formed on a bonded substrate, the sealing agent may be leaked during heating to cause contamination of the liquid crystal with the sealing agent.
Next, after the pixel substrate and the facing substrate are bonded together, UV light is applied by an UV irradiator to cure the above-described sealing agent, thereby to adhere the above-described pixel substrate and the above-described facing substrate to each other. After that, a cell cutting step and a final test step are performed. Thus, in the ODF method, after the liquid crystal is directly dropped onto the pixel substrate, both substrates are bonded together. Therefore, the ODF method has an advantage that the liquid crystal layer is formed in a shorter time, compared to the vacuum injection method.
Patent Documents 2 to 4 disclose configurations of typical liquid crystal displays.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2004-62138
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2001-21915
[Patent Document 3] Japanese Unexamined Patent Application Publication No. 2005-346100
[Patent Document 4] Japanese Unexamined Patent Application Publication No. 2006-227231